The present invention relates to a catalyst system and a process of preparing the same and uses of the same in ethylene polymerization and copolymerization processes.
Great efforts have been made in increasing the activity of ethylene polymerization catalysts and improving the properties of the product polymer and the production. Since 1970""s, Mitsui Petrochemical Industries, Ltd. and others have successfully developed varieties of magnesium chloride-supported Ti-Mg high active catalyst and led to a great development in the slurry polymerization technical field in world-wide. For example, JP 49-51378 discloses representative processes for ethylene polymerization and copolymerization. The catalyst used in these processes was prepared by the steps comprising mixing a grinded magnesium dichloride with ethanol in a lamp oil medium to form a MgCl2.6C2H5OH slurry and then adding diethyl aluminum chloride to consume most of ethanol through an esterification followed by the addition of titanium tetrachloride to obtain an Ti-Mg high active catalyst. The preparation technique of the catalyst was uncomplicated. The reaction conditions were not severe. And the operations were facilitated. However, several obvious disadvantages of this catalyst gradually appeared in the later practice. First, due to a large polarity difference between the solvents alcohols and alkanes used therein, it is difficult for the solvents to dissolve magnesium halide. In such a case, magnesium halide can not be dissolved completely to form homogeneous solution, even heated to higher temperature (e.g. above 100xc2x0 C.), but only a fine-grained colloidal suspension or a swelled magnesium halide slurry was formed. So the Catalyst thus prepared appeared some defects imparted by the characteristics of magnesium halide lamellar crystal, for example, the resultant polymer particles exhibit relatively low apparent density, poor particle morphology and poor particle size distribution.
CN 8510097.2 disclosed a catalyst system for olefine polymerization and copolymerization, and the catalyst system comprises (A) titanium-containing solid catalyst component, (B) alkyl aluminum compounds, and (C) organic silicon, wherein component (A) as a solid substance is obtained by dissolving magnesium halide into organic epoxy compounds and organic phosphorus compounds to form a homogeneous solution, then mixing with titanium tetrahalide or its derivatives, and in the presence of copreciptator such as organic anhydrides, organic acids, ethers, ketones and the like to precipitate a solid followed by treating with polycarboxylic ester to cause it to be supported onto the solid, and finally treating with titanium tetrachloride and inert diluent. The mixed solvent system used in the catalyst consisting of chlorine-containing epoxy compounds, organic phosphorus compounds and toluene was used to dissolve magnesium halide in place of alcohol and alkane solvent system. Owing to the similar polarity of those components discribed above, magnesium halide can be completely dissolved at a lower temperature (e.g. 50xc2x0 C.) and a homogeneous solution was formed. The defects related to the characteristics of magnesium halide lamellar crystal can be overcome, especially the apparent density, regularity and particle morphology etc. are remarkaly improved. When the catalyst system is used in propene polymerization, the catalyst system exhibits higher activity, and the resultant polymer exhibits high regularity and its particles has larger apparent denisity. However, when used in ethylene polymerization, the catalyst appears a disadvantage of low activity yet. For example, as desclosed in example 24, under the conditions of the temperature 85xc2x0 C., hydrogen pressure 0.25 MPa, ethylene pressure 0.75 MPa and ethylene polymerization for 2 hours, the polymerization activity of said catalyst is 537 kg PE/g Ti (10.7 kgPE/g Cat.), and the catalyst is not sufficiently sensitive to the molecular wight modification by using hydrogen as regulator (hydrogen modification). Owing to the defects described above, it is difficult to use the catalyst in industrial-scale.
The present invention provides a catalyst system suitable for use in ethylene polymerization and copolymerization and the process of preparing the same so as to overcome the disadvantages in the prior art. The present catalyst system for use in ethylene polymerization and copolymerization is prepared by dissolving an electron-donor activator in a solution of magnesium halide in a solvent system consisting essentially of organic epoxy compounds and organic phosphorus compounds to form a homogeneous solution, and then mixing with at least one coprecipitator and a transition metal titanium halide or its derivative to form a solid component, followed by incorporating in combination with an organic aluminum component prior to use in polymerizations. The preparation procedure of the catalyst system is uncomplicated. The catalyst exhibits high activity as being used in ethylene polymerization and the resultant polymer has better particle morphology and high apparent density, and with only small amount of low molecular weight byproduct being formed.
The catalyst system of the present invention for use in ethylene polymerization or copolymerization comprises components A and B. Said component A is a titanium-containing solid catalyst component obtained by dissolving an electron-donor activator into a solution of magnesium halide in a solvent system consisting essentially of organic epoxy compounds and organic phosphorus compounds to form a homogeneous solution and then mixing with at least one coprecipitator and transition metal titanium halide or its derivative. The electron-donor activator is at least one of organic alcohols, organic ethers and/or mixtures thereof; and the coprecipitator is selected from organic anhydrides, organic acids, ethers, and/or ketones. Said component B is an organic aluminum compound. The molar ratio of Al of component B to Ti of component A is from 5 to 1000.
The present invention further provides a process for preparing the catalyst system, particularly a process for preparing component (A) of the catalyst system.
The present invention also provides a method of using the catalyst system in ethylene polymerization.
The catalyst system of the present invention for use in ethylene polymerization comprises components (A) and (B) and optionally a metal halide adjusting agent.
Component (A) is a solid prepared by the following method:
Magnesium halide is first dissolved in a solvent system consisting essentially of organic epoxy compounds and organic phosphorus compounds, followed by mixing with an electron-donor activator to form a homogeneous clear solution. Then a coprecipitator such as organic anhydrides, organic acids, ethers, ketones and the like is added into the resultant solution, followed by mixing with trasition metal titanium halide or its derivative to from precipitate. Then the precipitate solids are filtered out, followed by washing with toluene and hexane to obtain a titanium-containing solid catalyst component (A).
Component (B) is an organic aluminum compound.
A metal halide adjusting agent is optionally used during the period of preparing component (A). Said metal halide adjusting agent is selected from a halide of Bi, Zn, Pb, Ca, Hg, V, Fe, Co and Sr or a mixture thereof.
1. Preparation of the magnesium halide solution
The magnesium halide solution is a homogeneous solution obtained by dissolving a magnesium halide in a solvent system consisting essentially of organic epoxy compounds and organic phosphorus compounds with or without other inert diluents, then adding an electron-donor activator to the solvent system.
Said magnesium halide of component (A) according to the present invention includes magnesium dihalide, complexes of magnesium dihalide with water or alcohol and the like, and derivatives of magnesium dihalide wherein a halogen atom is substituted by a hydrocarboxyl group or a halohydrocarboxyl group. Particularly, said magnesium dihalide is magnesium dichloride, magnesium dibromide and/or magnesium diiodide. The most preferred magnesium halied is magnesium dichloride.
The particle size of the magnesium halide used is preferred to be such that it is easily dissolved with stirring. The dissolution temperature is about 0xc2x0 C.-100xc2x0 C., preferably from 3xc2x0 C.-80xc2x0 C. Inert diluents such as hexane, heptane, octane, benzene, toluene, xylene, 1,2-dichloroethane, chlorobenzene and other hydrocarbons or halohydrocarbons can be added optionally into the solvent system; with benzene, toluene and xylene being preferred. The most preferred diluent is toluene.
Suitable organic epoxy compounds include oxides of aliphatic olefines, diolefines, halogenated aliphatic olefines, or diolefines, glycidyl ethers, inner ethers and the like having 2-8 carbon atoms. Examples of suitable organic epoxy compounds are ethylene oxide, propylene oxide, butylene oxide, butadiene oxide, butadiene dioxide, epoxy chloropropane, methylglycidyl ether, diglycidyl ether, tetrahydrofuran and the like. Ethylene oxide, propylene oxide and epoxy chloropropane are preferred, with epoxy chloropropane being the most preferred.
suitable organic phosphorus compounds include hydrocarbyl or halohydrocarbyl esters of phosphoric acid or phosphorous acid, e.g. trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl posphate, trimethyl phosphite, triethyl phosphite, tributyl phosphite, triphenyl phosphite, phenylmethyl phosphite and the like; with trimethyl phosphate, triethyl phosphate and tributyl phosphate being preferred, with tributyl phosphate being the most preferred.
Said electron-donor activator of component (A) according to the present invention, for example, is one or more organic alcohols including aliphatic alcohols or their corresponding isomer having 1 to 8 carbon atoms, for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, 2-ethylhexanol, n-octanol and glycerol, with ethanol, butanol, 2-ethylhexanol and glycerol being the most preferred. Examples of said electron-donor activator also include organic ethers, such as lower aliphatic ether, for example, methyl ether, ethyl ether, propyl ether, butyl ether and amyl ether.
During the period of preparing the homogeneous solution of said magnesium halide of component A according to the present invention, a metal halide adjusting agent can be added into said solution and said metal halide is selected from a halide of Bi, Zn, Pb, Ca, Hg, V, Fe, Co and Sr or a mixture thereof. The addition of said metal halide component in the catalyst system according to the present invention results in a more effective hydrogen-regulator modification on the molecular weight of the polymer in ethylene polymerization or copolymerization as said catalyst system being used.
The amounts of various ingredients of component A according to the present invention, based on per mole of magnesium halide, are as follows: organic epoxy compounds, 0.01-10 mole, preferably 0.02-4 mole; organic phosphorus compounds, 0.01-10 mole, preferably 0.02-4 mole; electron-donor activator, 0.005-15 mole, preferably 0.05-10 mole; metal halide, 0-0.2 mole, preferably 0.02-0.08 mole; coprecipitator, 0.02-0.8 mole, preferably 0.03-0.5 mole; and transition metal titanium halides, 0.2-20 mole, preferably 1-15 mole.
2. Precipitation of the solids
The magnesium halide homogeneous solution obtained by the above-mentioned procedure is mixed with titanium compounds to form a solid precipitate in the presence of a coprecipitator with stirring for a period of time at an elevated temperature.
Said coprecipitator of component (A) according to the present invention include organic acids, organic anhydrides, ethers, ketones or a mixture thereof; such as acetic anhydride, phthalic anhydride, succinic anhydride, maleic anhydride, pyromellitic dianhydride, acetic acid, propionic acid, butyric acid, acrylic acid, methacrylic acid, acetone, methyl ethyl ketone, benzophenone, methyl ether, ethyl ether, propyl ether, butyl ether, amyl ether and the like. The organic anhydrides are preferred, with phthalic anhydride being the most preferred.
The process of solids precipitation can be carried out by one of two methods. One method involves adding titanium compound into the magnesium halide solution at a temperature in the range of about xe2x88x9235xc2x0 C. to 60xc2x0 C. in dropwise, and precipitating the solids while the temperature is raised slowly to a range of about 30xc2x0 C.-120xc2x0 C., preferably 60xc2x0 C.-100xc2x0 C. The other method involves adding the magnesium halide homogeneous solution in dropwise into the titanium compound under the same conditions as the above to precipitate out solids. In both methods, a coprecipitator must be present in the reaction system. The coprecipitator can be added either after the magnesium halide solution is obtained or together with magnesium halide in step 1. Alternatively, two or more coprecipitators can be added simultaneously.
In order to obtain uniform solid particles, the process of precipitation should be carried out slowly. When the method of adding titanium halide dropwise is applied, the process should preferably take place over a period of from about 10 minutes to 6 hours. When the method of rising the temperature in a slow manner is applied, the rate of temperature increase preferably ranges from about 4xc2x0 C. to about 100xc2x0 C. per hour.
The liquid titanium compound or its derivatives used in this step can be in the pure liquid state, or in a solution of inert diluents, having the general formula TiXn(OR)4-n, wherein X is a halogen, R is a hydrocarbyl group being identical or different, and n is an integer of from 0 to 4. Examples of the compounds are titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, tetrabutoxy titanium, tetraethoxy titanium, chlorotriethoxy titanium, dichlorodiethoxy titanium, trichloroethoxy titanium and the like. Titanium tetrachloride is the most preferred.
The solid precipitate, after being separated from the mixture, is further washed with an inert diluent to remove ineffective titanium compounds and other impurities. The inert diluent herein used can be hexane, heptane, octane, 1,2-dichloroethane, benzene, toluene and other hydrocarbons.
Characteristics and chemical composition of the solid catalyst component (A)
Component (A) according to the present invention thus obtained through the above described steps, can be used as a solid or as a suspension.
The solid component (A) obtained according to this invention is in the form of powdered solid particles, with an average particle size of 2-25 microns, with a high specific surface area of more than 50 M2/g, preferably more than 200 M2/g. The particle size of component (A) can be controlled by alterating the preparing condition. The solid catalyst component (A) has the following chemical composition: titanium, 1.5-7.0 wt %; magnesium, 10-30 wt %; halogen, 30-75 wt %.
Component (B) is an organic aluminum compound, having the general formula AlRnxe2x80x2X3-nxe2x80x2, wherin R is hydrogen, or a hydrocarbyl group having 1-20 carbon atoms, preferably an alkyl, aralkyl or aromatic group and the like; X is halogen, preferably chlorine or bromine; and nxe2x80x2 is an integer of 0 less than nxe2x80x2xe2x89xa63. Examples of the compounds are trialkyl aluminums such as trimethyl aluminum, triethyl aluminum, tri-isobutyl aluminum, trioctyl aluminum; hydrogenated alkyl aluminums such as diethyl aluminum hydride, di-isobutyl aluminum hydride; halogenated alkyl aluminums such as diethyl aluminum chloride, di-isobutyl aluminum chloride, ethyl aluminum sesquichloride, ethyl aluminum dichloride; with triethyl aluminum and triisobutyl aluminum being preferred.
In the catalyst system according to the present invention, the molar ratio of Al of component B to Ti of component A is from 5 to 1000, preferably 100 to 800.
The process for preparing component A according to the present invention comprises the steps of:
(a) dissolving an electron-donor activator, and optionally, a metal halide adjusting agent, with continuously stirring into a solution of magnesium halide in a solvent system consisting essentially of organic epoxy compounds and organic phosphorus compounds to form a homogeneous solution;
(b) either adding in dropwise a titanium compound into said homogeneous solution or adding in dropwise said homogeneous solution into the titanium compound in the presence of a coprecipitator at a temperature of about xe2x88x9235-60xc2x0 C., preferably xe2x88x9230-5xc2x0 C., and then raise the temperature of the reaction mixture to 60-110xc2x0 C. to form a suspension;
(c) stirring said suspension for 10 minutes to 10 hours;
(d) filtering out the precipitate formed from said suspensions, removing the mother liquid and washing the solid substance with toluene or hexane to obtain a titanium-containing solid catalyst component.
Component A and component B of the catalyst system according to the present invention can be used in polymerization system directly, or can also be used in a pre-complexed form.
The catalyst system according to the present invention is used in the homopolymerization of ethylene and can also be used in the copolymerization of ethylene with other oldfines. The suitable comonomer includes propylene, butene, pentene, hexene, octene, 4-methylpentene-1.
Liquid-phase polymerization and gas-phase polymerization can both be employed. An inert solvent selected from saturated aliphated or aromatic hydrocarbons such as hexane, heptane, cyclohexane, naphtha, extract oil, hydrogenated gaoline, kerosene, benzene, toluene and xylene can be used as the reaction medium in liquid-phase polymerization. Prepolymerization can be conducted before polymerization. Polymerization can be carried out in batch mode, semi-continuous or continuous mode.
The polymerization takes place at a temperature ranging from room temperature to about 150xc2x0 C., preferably from about 50xc2x0 C. to 100xc2x0 C. Hydrogen gas can be used as a molecular weight regulator to regulate the molecular weight of the polymer.